This invention relates to an apparatus for establishing a flow of a fluid mass, such as a stream of gas, to serve as a wind tunnel or to predict the actual lifetime and reliability of metal electronic components.
Electrolytic metal migration and corrosion are common reliability problems encountered in the microelectronics industry. Accelerated metal migration and corrosion investigations are performed in test chambers in which the temperature, humidity, pollutant concentration, air velocity, and applied bias can be varied or cycled. Typically, little attention is paid to velocity or concentration profiles as gradients in these chambers. Most accelerated metal migration and corrosion laboratory tests are performed in test chambers which have unknown or uncontrollable velocity and concentration gradients.
Known accelerated test chambers utilized in metal migration and corrosion studies are usually classified as one of three types: (1) flow-through chambers, (a) commercial humidity cabinets, and (3) sealed containers. The flow-through chambers are usually constructed of glass, plastic or poly(tetrafluoroethylene) and best suited for studies using humidified pollutant gases. It is possible, when using a flow-through chamber, to mix humidified air and pollutants in the test chamber. However, this does not provide consistent pollutant and water concentrations in the chamber. Alternatively, the humidified air and pollutant gas streams can be mixed before introduction into the test chamber.
Conventional flow-through chambers are rectangular in shape. Rectangular chambers exhibit velocity gradients, stagnant regions in the corners, and eddy currents at the entrance and exit that may cause nonuniformity of velocity, water vapor and pollutant concentrations.
Reports in the literature indicate that the rates of corrosion of silver, copper and of copper migration are dependent upon the gas velocity past the specimens. However, accelerated test chambers are not standardized, and it is difficult to compare metal migration and corrosion studies performed in different chambers.
Carbone and Corl in "Atomspheric Corrosion", W. H. Arbor, Editor, pp. 173-175 John Wiley & Sons, New York (1982), have developed a test to predict metal migration and corrosion. It involves a drop of 400 average molecular weight polyethylene glycol (PEG-400) between a pair of biased electrodes. The PEG film absorbs water and gaseous pollutant species from the ambient environment. These species ionize in the PEG or PEG water film, causing an increase in the electrical conductivity of the film. Copper ions are formed at the anode and migrate to the cathode where they are reduced, producing dendrites. When the dendrites form a continuous filament between the electrodes, the device shorts. The time for the electrode system to short is a measure of the relative rate of metal migration. The metal migration rates for this accelerated test are moderate. The short times are longer than the water drop test, another standardized test, and much shorter than exposing dry electrodes to a temperature-bias-humidity test with or without pollutants. This type of test can be conducted in the accelerated test chamber of the present invention.
According to this invention, an apparatus is provided to distribute uniform quantities of gas so that the apparatus can function as a wind tunnel and to provide a section for establishing uniform gas velocity profiles and pollutant gas concentration profiles to enable the apparatus to function as an accelerated test chamber.